The proliferation of customer owned telephone equipment and equipment ancillary thereto (e.g. burglar alarms, telephone answering devices, etc.) has increased the likelihood of malfunctions. As a consequence, the question of whether the fault is in the telephone company equipment and network or in the subscriber's equipment and network, is occurring with increasing frequency.
As a practical matter, the telephone company is required to bear the initial burden of isolating the fault whether it occurs in the company's equipment or in the subscriber's equipment. Often this entails a visit to the subscriber's premises.
To mitigate this burden apparatus has been proposed for isolating the telephone company network from the customer's equipment and lines by remote signalling from the central office so that tests can be conducted at the central office or other convenient locations to determine whether the fault lies with the subscriber's equipment or the utility's networks and equipment. Such a system is shown in the U.S. Pat. No. 3,725,613.
In that system an RC network is employed at the disconnect point between the phone company network and the subscriber's system. A remotely generated switching pulse charges the capacitor and initiates current through the coil of a switching relay the contacts of which provide the disconnect switching. The relay coil is maintained energized for a period after the termination of the switching pulse by reason of the discharge of the capacitor.